Current gene therapy tools (e.g., viral-mediated gene-addition) rely on the provision of functional copies of a therapeutic gene that integrate at random or semi-random into the genome. The consequences of the random integration are perturbation of the locus where the cargo lands and potential gene inactivation or dysregulation (off target effects). These can result in life threatening side effects to the patient.
Duchenne muscular dystrophy (DMD) is a common, genetic neuromuscular disease associated with the progressive deterioration of muscle function, first described over 150 years ago by the French neurologist, Duchenne de Boulogne, after whom the disease is named. DMD has been characterized as an X-linked recessive disorder that affects 1 in 5,000 males caused by mutations in the dystrophin gene. The gene is the largest in the human genome, encompassing 2.6 million base pairs of DNA and containing 79 exons, with mutations scattered across most exons. The dystrophin gene is located in the subregion 21 of the short arm of the X-chromosome. (Roberts, R G., et al., Genomics, 16:536-538(1993)). The transcript of the dystrophin gene is spliced into the mature 14 kb mRNA. The dystrophin gene is located in the subregion 21 of the short arm of the X-chromosome. The transcript of the dystrophin gene is spliced into a mature 14 kb mRNA.
Approximately 60% of dystrophin mutations are large insertion or deletions that lead to frameshift errors downstream, whereas approximately 40% are point mutations or small frameshift rearrangements. The vast majority of DMD patients lack the dystrophin protein. No drug is so far available for effective treatment of DMD, and therefore development of a drug for its treatment has been longed for by patients across the world. In 1987, dystrophin gene, the causative gene of DMD, was found by means of retrospective genetics, and Becker Muscular Dystrophy (BMD) also was found to result from abnormality in the same dystrophin gene (Koenig, M. et al., Cell, 50:509-517(1987)).